The biggest, living thing that exists on this planet is a plant. Like this giant Sequoia tree（巨杉） in California.

Plants, whether they are enormous like this one, or microscopic, are the basis of all life, including ourselves. 

We depend upon them for every mouthfulof food that we eat, and everylungful of air that we breathe.

(资料图片)

Plants flourish in remarkable ways. Yetfor the most part, the secrets of their world have been hidden from us. Until now.

for the most part:在极大程度上，多半

Now, we have new ground-breakingtechnology that enables us to enter their extraordinary world and see their lives from their perspective.

This series will reveal the extraordinary and dramatic ways in which plants behave. And we will explore the challenges demanded by the very different landscapes in which they live.

The tropics. The richest and most competitive place in which to survive.

The bizarre water world. Where giants fight ferociousbattles and plants eat animals - alive!

Deserts. The world of extremes.

Seasonal lands...where survival depends on precision timing.

And everywhere we will explore the critical and intimate relationships between plants and animals, including ourselves.

Join me in a world that takes you by surprise. See our planet as never before from the plants' perspective.

This is The Green Planet.

Tropical Worlds

I'm in Costa Rica（哥斯达黎加）, in the heart of a rainforest, the richest and most dynamicenvironment on Earth. Rainforests only cover a very small proportion of the Earth's surface, yet they contain over half of all known species of animals and plants.

Up here, the forest's canopy is bathed by life-giving sunlight. The branches of the great trees carry rich, flourishing, sky-gardens, home to countless different kinds of beautiful plants. Each species has evolved its own exquisite solution to the chanlleges of survival.

This forest-world may look peaceful, timeless and unchanging, but that is far from the truth!

This is a battlefield.

Throughout this forest, plants are competingferociously with one another, to claim the light. The battle is at is fiecest on the forest floor where only two percent of the sunlight filters through. Plants here have to bide their time. Their opportunity comes when an old tree dies.

When that happens, sunlight floods the forest floor, for the first time in, perhaps, a hundred years.

A Seedling's wait is over! It must now race skywards and claim a place in the canopy.

But it's not alone. Rivals are everywhere, each with its own survival strategy.

Some plants like this Monstera（龟背竹属植物） stretch out divided leaves to collect what light they can. 

This vine isgropingblindly around with its tendrils. It attempts to reach the light by hitching a ride. Its tendrils are highly sensitive to touch, and a suitable target is in range.

grope: to feel about blindly or uncertainly in search

tendril: a leaf, stipule, or stem modified into a slender spirally coilling sensitive organ serving to attach a climbing plant to its support

hitch a ride: 搭便车，顺风车

Got it!

The vine tightens its grip and begins to haulitself upwards. But it's now overtakenby the forest's fastest-growing tree, a young balsa（轻木）. Its giant leaves are already 40 centimetres across and are stealing the light from its rival below.

But the balsa's battle is not yet won. Other different vines are lying in wait. 

Each is armed with dozens of claw-like hooks. If just one hook gets a grip, the vine will be able to smotherits victim.

smother: to kill by depriving of air  

But the balsa is defended by a shield of slipperyhairs. The vine's hooks just can't get a hold. The balsa brushes them aside, and continues to rush skywards, leaving the losers in its shadow to fight among themselves. This balsa has won its battle for the light and it's done so in a little over a year!

Most trees would have grown an inch or so in that time, but this one is already 30 feet, 10 metres tall.

Balsas owe their success tothe special character of their wood.

If this section of tree trunk came from a hardwood tree, it would be really quite heavy. But as it is, it's from balsa, and it's really very light, and that's because of its internal structure.

Under the microscope, balsa wood looks like a honeycomb（蜂窝）. It contains more air than wood. So not only can it grow very fast, but it gets the maximum height for minimum weight. But fast growth needs something else, fuel, and lots of it. That fuel is created in a plant's leaves as they soak up the sun. It's a process called photosynthesis. A chemical reaction that is the basis of all life on earth. 

Leaves are covered by thousands of microscopicpores called stomata（气孔）. When open, they extract carbon dioxide from the air, and using energy from the sun, combine it with nutrients to build the plant's tissues. And, critically for us, the process releases the oxygen that we, and all animals, need in order to breathe.

But for plants there is a downside. These precious, energy-packed leaves attract predators in every shape, size and agility.

agility: the quality or state of being agile

A sloth（树懒） can only move slowly, but you don't need speed to gather leaves and it eats nothing else.

The plants here are under constant attack from all kinds of leaf eaters, but the most voracious by far is hardly ever seen. It consumes 50,000 leaves every day. It's created this great clearing in the forest and it lives just beneath my feet.

voracious: very eager for something, especially a lot of food  

clearing: an area in a wood or forest from which trees and bushes have been removed

It's called Leucoagaricus（白环菇属）. It's neither animal nor plant. It's a fungus! It lives five metres underground, far from the leaves that it devours. To get them, it employs the best leaf-gatherers in the tropics.

Leafcutter ants（切叶蚁）.

Millions of them provide the fungus with its food, and in return, the fungus cultivates tiny mushrooms as food for the ants. The fungus releases chemical signals that tell the worker ants what type of leaf it wants to eat.Scoutsare sent out with the latest orders.

Worker ants will travel hundreds of metres to find the right kind. Today's crop is being taken from a young Bixa tree（红木属植物）. Just a few years old and still battling to reach the canopy, it can ill afford to lose any of its leaves.

Between them the ants can demolish a large leaf in a matter of minutes. The sound of cutting attracts more ants. Now, the pieces are carried back to the underground fungus.

The ants can run at speeds of two metres a minute. And each can carry a load ten times its own weight. It's a river of leaves across the jungle floor, part of a vast network that extends for miles through the forest.

To avoid congestion, worker ants digtrenchesaround obstacles.

trench: a narrow hole that is dug into the ground.

Thousands of pieces are delivered every hour to the waiting fungus.

Fed by such a continuous supply, the fungus grows rapidly, filling the chambers in which it lives. So, the ants excavate more space. It seems that the fungushas the upper hand, and the Bixa tree will not survive.

But it fights back, using chemical warfare. The Bixa tree floods its leaves with toxins that could kill the distant fungus. As the ants carry the fragments back they are, themselves, poisoning the fungus on the tree's behalf. It's a long distance attack!

warfare: an activity undertaken by a political unit(such as a nation) to weaken or destroy another

As the poison takes effect, the ants sense that their fungus is weakening, and they respond to its signals by changing to another source of leaves. So the plant's chemical response forces the ants to constantly switch from tree to tree.

Strike and counterstrike.

And that ensures that enough leaves remain uneaten for each tree to recover.

Once a plant becomes adult, it can switch its energies from growth, to reproduction.

The tropical forests of the America stretch fromMexicoto the southern reachesof the Amazon. They contain more than 100,000 different species of plant. Each with its own particular survival strategy. 

One species, that has adopted a grow-fast lifestyle, flourishes throughout this vast region.

The balsa.

But it has to pay a high price for doing so. The light-weight wood that enables it to grow at such speed is not strong and is easily broken. Few balsas live longer than twenty years. This one is approaching the end of its brief life. So the time has come for it to reproduce.

It has used a huge amount of energy to produce some of the most extravagantflowers in the forest in immense numbers. Each is the size of a human hand. As night falls, the tree prepares anenticing treat.

enticing: arousing strong attraction or interest

This is a kinkajou（蜜熊）, a kind of fruit-eating raccoon（浣熊）. 

Each flower is filled with huge quantities of exceptionally rich nectar, superchargedwith sugar.

supercharge: to charge greatly or excessively(as with vigor or tension)

Irresistible!

The kinkajous drink so greedily that they get pollen（花粉） all over their faces. So, as they move from tree to tree, they carry pollen with them.

But the balsa leaves little tochance. The nectar might appear to have run out, but this is just the first round. Now the balsa refills its flowers, enticingthe kinkajous back, to repeat the process. Seven times a night! Pollinationis complete.

chance: to accept the hazard of: RISK

entice: to attract artfully or adroitly or by arounsing hope or desire

And the kinkajous? They alsoget well servedwith over a hundredpints（品脱） of nectar in just a few weeks.

Both plant and animal do well out of this arrangement. But in the tropical world that isn't always so.

Borneo（加里曼丹岛）.

Here, on the slopes of Mount Kinabalu, live plants that eat animals using pitcher-shaped leaves full of water.

pitcher:a container for holding and pouring liquids that usuallt has a lip or spout and a handle.

Insects are attracted by the expectation of nectar but tumbleinto the pitcher, where they're drowned and absorbed.

tumble: to fall suddenly and helplessly

On the lower slopes of the mountain, a plant grows that has no leaves at all, or even a stem! All that can be seen is this, a bud.

It is a parasite!

The rest of its body lies within the tissues of a liana（藤本植物） on which it feeds. After about five years, the bud finally opens into amonstrousflower. It now has only a day or so in which to be pollinated before it starts to wither. 

Its petals are the colour of the blood. Their surface is tough and warty（有疣的）. It appears to have fur. Even whiskers（胡须，腮须）and teeth. At first sight, it might be mistaken for a dead animal. This is Rafflesia（凯氏大王花）, the corpse flower.

A metre across, it's the world's biggest flower, and this one is a male. From its centre comes the pungent odour of death. It's a scent that might not appeal to every animal, but it's very attractive to carrion flies（丽蝇）. They lay their eggs on rotting flesh. The scent lures the fly deep into the flower in search of meat. 

pungent: have an intense flavor or odor

The fly finds nothing. The Rafflesia, however, has the fly exactly where it wants it. It's stuck pollen to the fly's back.

If this male Rafflesia's strategy is to work, the fly carrying its pollen must now visit a female corpse flower, such as this one.

Success!

Once pollinated, plants are able to produce seeds, the next generation, but once again, there are animals all over the forest, that are eager to make a meal of them.

The Malay archipelago（群岛）. A vast tropical world of a thousand islands.

It's home togiants, the tallest trees in the tropics, many of which live for centuries. They produce seeds in enormous numbers, but only do so when the time is right.

This individual hasn't produced a single seed for nearly a decade. But in the last weeks, it has become festooned, with more than ten thousand of them. Each seed has the potentialto produce a giant like its parent. But success will depend on timing.

festoon(n.): a decorative chain or strip hanging between two points.

festoon(v.):  to hang or form festoons on

Seed-hunters are gathering. Bearded Pigs（婆罗洲须猪）.

But these seeds have been produced by a dipterocarp（龙脑香科植物）. Trees that create the tropical world's largest seed nursery. After years of waiting, thousands upon thousands ofindividual dipterocarps have synchronisedto produce the next generation all at the exactly the same time. 

thousands upon thousands of: 成千上万

Now these seeds will face the dangers below, together.

By releasing billions of seeds all at the same time, theyswampthe pigs and any other animals with more than they could possibly eat. And thatbuys timefor some of the seeds to take root and sprout.

swamp: to overwhelm numerically or by an excess of something:FLOOD

The tree's strategy has worked. But a seedlingwill have to overcome many more dangers over the years, if it too is to become a giant! 

And there are many ways in a tropical forest by which a tree's life can be ended before it reaches its prime.

The northernmost tip of Australia. This is the world's most ancient rainforest. 

Battles between animals and plants have ragedhere for 180 million years. So the plants have had time to develop effective defences.

rage: to prevail uncontrollably

This is a poison-arrow tree（见血封喉树）, one of the tropical world's most heavily defended plants. Its trunk is tall and slippery, and exudesa poisonous sap. It appears to be almost invulnerable. But even so, just as this individual reaches maturity, its life has become endangered.

exude: to exude is to produce from the inside and spread out slowly

Each monsoon（季风）season, it is invaded from above. It attracts hundreds of Shining Starlings（群辉椋鸟）. Its immense smooth trunk makes its high branches above a safe place to nest. But over the years, this has created a major problem for the tree.

After feeding, the starling return to the nest to digest their food with inevitable consequences.

Every year they produce almost a quarter of a tonne of droppings. The toxic chemcals they contain createa dead zone that completely surrounds the tree.

The toxins are absorbed by its roots and travel up through the trunk and into every leaf. Branch by branch, the tree is slowly dying.

It has become a victim of its own success.

It has been poisoned.

Now a new battle begins - one to claim the tree's dead body and the vast amount of nutrients that it contains. It's a battle that is fought throughout the natural world, involving a group of organisms that we rarely notice.

Here on the floor of a tropcal forest. It's dark, it's humid and it's hot. Ideal conditions for fungi. We normally think of fungi as things like this - mushrooms of one kind or another. But these are just the fruting bodies（子实体）. They exists for most of the time hidden in the leaf litter（落叶层） and the earth as a network offine white threads.

fine: a very thin in gauge or texture

The threads of competing fungi envelop their victim's body, releasing enzymes which digest the tree's tissues and unlock the nutrients within. There are a million or so different species of fungi in the tropics. Somefeed on dead plants. Others eat them alive. And some reveal their existence in aneerilybeautiful way.

envelop: to enclose or enfold completely with or as if with a covering

eerily: in a strange and eerie manner

In Africa - in the Congo（刚果） - this is known as Chimpanzee Fire. The mysterious bioluminescent glow becomes brighter as the fungus digest the tree. When fungi have fed sufficiently, they develop their reproductive organs.

Each can produce literally billions of spores, the tiny particles thatcarry the species' genetic blueprint. Each spore like this, has the potential to kill a tree.

The spores are so light. They can be carried by the slightest air currents. At least a billion float above every square metre of rainforest. Recently it has been discovered that these spores do far more than just bring death and decay. They are, in fact, at the very centre of the rainforest's life-support system.

High in the humid air, the spores combine with molecules of water. Gradually they collect into droplets, which, when they are heavy enough, fall as rain. 

Over two and a half metres of rain falls every year in a rainforest. And in the centre of almost every raindrop, there is afungal spore!

The world's rainforests are the richest and most dynamic environments on Earth, built on complex connections and relationships. But these connections, competitive or collaborative, are now becoming increasingly fragile.

When Charles Darwin was exploring the tropical world nearly 200 years ago, he wrote this in his diary:

Among the scenes which are deeply impressed on my mind, none exceed insublimitythe primeval forestsundefaced by the hand of man.

sublime: tending to inspire awe usually because of elevated quality(as of beauty, nobility, or grandeur) or transcendent xcellence

sublimity: the quality or state of being sublime

He would struggle to find such a place today.

Today, 70% of all the world's rainforest plants grow within a mile of a road or a clearing that we have cut into the forest. And this is creating new battlefields in the tropical world. Alien armies of identical cultivated plants now stand where thousands of different species once grew.

We have planted vastregimentsof crops in order to provide ourselves with food and other commodities, and the ancient forest has been reduced to, ever fewer, isolated fragments. All, however, is not lost. The fragments can still be sanctuaries, keepiing alive the intimate relationships within them. Their size, is nonetheless critical.

This is the Seven-hour flower（灯蝠花）.

This plant produces its flowers at night. They open about 6 o'clock, and each blossom only lasts that night. It opens for about 7 hours and then it dies. But during that time, it provides food for one particular animal. A bat, and here it is.

During the 7 hour flower's flowering season, Underwood's Bat feeds almost exclusively on its nectar. It is the plant's primary pollinator. 

It might seem that this is a fairly evenly balanced relationship, but not so. The bat likes this nectar because it's sweet, but it's not very nourishing. 

nourishing: A nourishing drink or food makes you healthy and strong

So the bat must visit hundreds of flowers a night, and it pollinates them as it feeds. But if a patchof forest becomes too small with too few flowers, the bats will disappear, and without the bats the flowers can't reproduce and will soondie out. The partnership is broken.

Life in the forest depends on countless close relationships, but they are increasingly under threat as forests become more fragmented. The solution, of course, is to join these remaining fragments together again.

Thirty years ago, I came to this exact spot. This land belonged to a scientific research establishment and it was covered with grass being grazed by cattle. The scientists got rid of the cattle and allowednature to take its course. Just look at it now.

let nature take its course:顺其自然，任其自然发展

This new forest has become a bridge that connects several fragments, allowing plants and animals to both renew old connections and create fresh ones. Of course, we urgently need to protect what healthy forests still remain. Butlooking forward, we must take what may well be our last chance to re-establish the lost forests and help the tropical world to heal itself.

It will take the cooperation of nations around the world. But it is the only way in which we will be able to preserve the treasures of the tropical forest for future genarations, and with it,  ultimately protect all life on this, our Green Planet.  

look forward:展望未来